The filter capacitor C connected in the DC side of diodes bridge rectifier was removed. By using pulse width modulation ( PWM) method and current loop, energy conversion from AC to DC was realized, performance of the power supply was upgraded, the harmonic currents was restrained, the current in the AC sidewas made to be of good sinusoidal shape and the converter of unify power factor was insured. After theoretical analysis of the operating principle, simulations was carried out to ver-i fy the theoretical result. A microcomputer based control system, which was used to trigger the gates of IGBT and realize the strategy of control, was also provided.